Here are 2 different patients with similar findings. The top image is a diffusion weighted body MRI in a patient with liver metastases from breast cancer. The patients bone marrow is dark on this negative image indicating restricted diffusion. Restricted diffusion occurs in regions of increased cellular density. The second (middle) image is a whole body PET/CT in a patient with lymphoma. A pre chemo PET/CT is displayed above a post chemo PET/CT. Note the diffusely increased FDG uptake in the marrow space indicating increased glucose metabolism. Note also a significant response to therapy. The patients were both receiving GCSF which increases Bone marrow cellular density and metabolism.